10mm Stars Straw Cover for Stanley Cup are made of safe, non-toxic, and odorless silicone. They provide a good sealing effect, are sturdy, and can be reused many times. Simply rinse with clean water after use. These straw covers have an inner diameter of approximately 0.39 inches (1 cm), making them a perfect match for most straws with a diameter of 9-10 mm (0.35-0.39 inches).